I too would like to know the answer to the above questions.
I've got a 523, haven't had it for long nut all I know is that it isn't very economic with city driving. I avg around 450kms per tank city an 800kms country driving. Upon inspection last week we found that both my O2 sensors Pre cat are stuffed and not working, so she's running rich and using alot more fuel than normal. The headlights can be hanged quite easily an done at home with a good tool set - I believe it just involves replacing the entire housing to an updated angel
eyes kit. You will probaly have to get a full HID kit wired an installed as they don't come factory from what I know.

I've only had my car a little while so I could
be wrong about the lights - can anyone else confirm/deny this and provide us with more information?

Used to drive a 523i e39 tiptronic. sold it to a family member. really good car still no complaints what so ever. (bought myself a 525tds e39). drove the 523ia for 11000 km / approx 6800 miles and with every tank i filled i calculated my mpg.

9.65 L / 100 km OR 24.3 mpg
only mod. i did was silencer delete.
(first with k&n conical filter but fitted original again)
nice growl in low rpm acceleration

best mpg i ever had on one tank was 26.3 mpg with aceton
always did 650 km + with one tank.

Hi guys, I also in need of getting information on the E39 523i, planning to get my self a E39 523i (Manual only as 523i kind of rare here in indonesia and most of them i see in person only have manual tranny) ...

What do you think about the power to weight ratio? i mean is it good enough? does it fun to drive also? i currently own an E34 M50TUB20 and its fun (I know the B20 is underpower but at least its a fun car to drive)